For me, I think I started noticing the "blown pupils" thing sometime after the summer of 2010; it was after I wrote my Hetalia fic, 'Love Is A Higher Law', in which I described basically the same thing but at the time there wasn't a stock phrase to get it across, so I wrote "That," America stared up at him with eyes so dilated they were almost black, barely ringed with blue, "was amazing."

I feel like a while after that, I started seeing "blown pupils" hither and yon, and realized it was supposed to mean the same thing I had tried to describe earlier.